I. Field of the Invention
The present invention relates to the field of magnetic memory systems for the storage of binary digital data and in particular to magnetic memory systems that store binary digital data as the presence or absence of a magnetic domain in a thin ferromagnetic film layer.
II. Description of the Prior Art
The utilization of thin ferromagnetic films of approximately 81% Ni-19% Fe of approximately 350 Angstroms (.ANG.) thick has been known since the early 1960s. Such thin ferromagnetic film memories may be formed by the evaporation or deposition process disclosed and claimed in the S. M. Rubens U.S. Pat. No. 2,900,282 and organized in the S. M. Rubens, et al U.S. Pat. No. 3,030,612 to form a multi-plane magnetizable memory system. Such technology later evolved to the utilization of electrically-alterable, random access memory systems that utilize the Mated-Film elements of the R. J. Bergman, et al U.S. Pat. No. 3,435,435.
Much later work in the area of thin ferromagnetic films resulted in the development of nondestructive readout, random access cross-tie wall memory systems such as exemplified by the L. G. Zierhut, et al U.S. Pat. No. 4,473,893. Such a cross-tie wall memory system has many advantages in that the discrete memory elements are a small size, each 10 microns (.mu.m) in width and 15 .mu.m in length, the small size of which permits the packaging of a three dimensional random access memory system that is both nonvolatile, e.g., retains its stored information upon the loss of power coupled thereto, and is substantially impervious to radiation.
However, such a cross-tie wall memory system does have a serious disadvantage in that its output signal, upon the detection of a stored 0 and a stored 1, is a function of the change in resistivity of the memory element because of the presence, vel non, of a crosstie, Bloch-line pair representing a stored 1. This change of resistivity of the cross-tie memory element produces two output signals of relatively small difference. Accordingly, it is desirable that there be provided a memory system having the desirable characteristics of the cross-tie wall memory system while providing a memory element that provides a significantly higher difference signal upon readout of a stored 0 or of a stored 1. The present invention is directed towards such a memory element.